System and method for monitoring chemical mechanical polishing

ABSTRACT

An apparatus for chemical mechanical polishing of a wafer includes a process chamber and a rotatable platen disposed inside the process chamber. A polishing pad is disposed on the platen and a wafer carrier is disposed on the platen. A slurry supply port is configured to supply slurry on the platen. A process controller is configured to control operation of the apparatus. A set of microphones is disposed inside the process chamber. The set of microphones is arranged to detect sound in the process chamber during operation of the apparatus and transmit an electrical signal corresponding to the detected sound. A signal processor is configured to receive the electrical signal from the set of microphones, process the electrical signal to enable detection of an event during operation of the apparatus, and in response to detecting the event, transmit a feedback signal to the process controller. The process controller is further configured to receive the feedback signal and initiate an action based on the received feedback signal.

RELATED APPLICATIONS

This application claims priority of U.S. Provisional Patent ApplicationNo. 62/585,182 filed on Nov. 13, 2017, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to chemical mechanical polishing methods used insemiconductor manufacturing processes, and an apparatus for chemicalmechanical polishing.

BACKGROUND

Size of critical features in an integrated circuit (IC) has continuallydecreased, and the need to perform high resolution lithography processesgrows. As a consequence, the depth of focus of the radiation used forlithography has also decreased. There is a need to control the precisionof planarization of wafers at atomic scale. For example, typicaldepth-of-field requirements for 28 nm, 22 nm, 16 nm and 10 nm technologyare approaching angstrom levels. These are, of course, merely examplesare not intended to be limiting.

While CMP is most commonly used during wafer fabrication to provide anatomically flat surface at the beginning of the lithography process, aslithography has evolved and complexity of lithography increased, otherareas of use for CMP have developed. For example, lately, CMP is used toplanarize shallow trenches by polishing metal layers such as aluminum,copper and tungsten, etc.

Despite the increase in versatility of CMP, the traditional issues withCMP remain. For example, CMP can introduce mechanical defects in wafersbecause of the use of mechanical force while polishing. The polishingpads can create and/or release coarse particles which can cause ascratch on a wafer being polished. Additionally, for many types ofsurfaces the CMP process requires a “blind” endpoint detection. Forexample, monitoring of the CMP process has required periodic opticalobservation of the wafer during the CMP process. This results insubstantial down-time for the process, and also has the potential toreduce yield if defects go undetected under manual observation. Improvedtechniques for online monitoring and control of CMP are, therefore,desired.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a schematic view of an apparatus for chemical mechanicalpolishing (CMP), in accordance with an embodiment.

FIG. 2A is a schematic view of CMP process in normal operation andsimulated time and frequency domain plots of sound emanating from theprocess, in accordance with an embodiment.

FIG. 2B is a schematic view of CMP process in abnormal operation andsimulated time and frequency domain plots of sound emanating from theprocess, in accordance with an embodiment.

FIG. 2C illustrates an overlay of the time and frequency domain plots ofsound emanating from a normal CMP process and an abnormal CMP process,in accordance with an embodiment.

FIG. 3 is a schematic view of an apparatus for monitoring a CMP process,in accordance with an embodiment.

FIG. 4 depicts an illustrative flow chart for a method of monitoring aCMP process, in accordance with an embodiment.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus/device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly. In addition, theterm “made of” may mean either “comprising” or “consisting of.”

The present disclosure generally relates to methods and apparatuses formonitoring and controlling a chemical mechanical polishing (CMP) processused in semiconductor manufacturing. More particularly, the methods andapparatuses described herein facilitate monitoring a CMP process foranomalous behavior. Wafers are typically planarized using the CMPprocess which uses a polishing pad and a chemical slurry. The slurry istypically a colloid of a material that acts as a chemical etchant foretching the material at the top surface of the wafer. The polishing padis rotated relative to the wafer while slurry is disposed so as toremove material and smooth any irregular topography. The CMP apparatusis not amenable to direct optical inspection during the process.Monitoring of the CMP process is, therefore, performed by periodicallystopping the process and inspecting the wafer, to determine whether anendpoint has been reached. Additionally, any anomalous outcome, e.g., amicro-scratch on the wafer surface, is only detected after stopping theprocess and inspecting the wafer which may be too late to takecorrective action. This results in a substantial bottleneck in theoverall semiconductor manufacturing process, and affects themanufacturing yield. Embodiments of the apparatuses and methodsdescribed herein are expected to facilitate monitoring and control ofthe CMP process during operation without stopping the process, therebyincreasing the speed and yield of the CMP process.

FIG. 1 schematically illustrates an apparatus for performing chemicalmechanical polishing on a semiconductor wafer, in accordance with anembodiment of the present disclosure. In an embodiment, the apparatusincludes a chamber 100 enclosing a rotatable platen 110, a polishinghead assembly 120, a chemical slurry supply system 130, and a padconditioner 140.

In an embodiment, the platen 110 is connected to a motor (not shown)which rotates the platen 110 at a preselected rotational velocity. In anembodiment, the platen 110 is covered with a replaceable polishing pad111 (interchangeably referred to herein as “the pad”) of a relativelysoft material. In some embodiments, the pad 111 is a thin polymeric discwith a grooved surface, and can be porous or solid, depending on theapplication. Factors determining the material and physical properties ofthe pad 111 include the material to be polished (i.e., material at thewafer surface), and the desired roughness after polishing. The pad 111may have a pressure sensitive adhesive on the back so that the pad 111adheres to the platen 110. During the polishing process, the pad may bewetted with a suitable lubricant material, depending on the type ofmaterial being polished (i.e., the material at the top surface of thewafer).

In an embodiment, the polishing head assembly 120 includes a head 121and a carrier 122. The head 121 holds the carrier 122 which in turnholds a wafer 123 to be polished. In some embodiments, the assembly 120includes a displacement mechanism (not shown) to oscillate the head 120sideways (with reference to FIG. 1 ). In some embodiments, the head 121may include a motor for rotating the wafer 123 relative to the platen110. In some embodiments, the wafer 123 and the platen 110 are rotatedin an asynchronous non-concentric pattern to provide a non-uniformrelative motion between the platen 110 and the wafer 123. Thenon-uniformity of the relative motion facilitates uniform removal ofmaterial from the wafer surface by avoiding repeated removal from thesame spot. The assembly 120 applies a controlled downward pressure tothe wafer 123 to hold the wafer 123 against the platen 110.

The slurry supply system 130 introduces a chemical slurry 135(interchangeably referred to herein as “the slurry”) of a suitablematerial to be used as an abrasive medium between the pad 111 and thewafer 123. In an embodiment, the slurry 135 is a colloid of abrasiveparticles dispersed in water with other chemicals such as rustinhibitors and bases to provide an alkaline pH. In some embodiments, theabrasive particles are of materials such as, for example, silica, ceria,and alumina. In an embodiment, the abrasive particles have a generallyuniform shape and a narrow size distribution, with average particle sizeranging from about 10 nm to about 100 nm or more depending on theapplication for which it is being used. In an embodiment, the slurrysupply system 130 includes a storage system (not explicitly shown) and aconduit 131 for delivering the slurry 135 to the polishing pad 111 atopthe platen 110. The rate of flow of the slurry 135 may be controlledbased on the application.

In an embodiment, the pad conditioner 140 periodically “conditions” thepolishing pad 111 to provide uniform thickness and roughness across theentire area of the platen 110 by polishing the pad 111. Maintaining thethickness and roughness of the pad 111 prevents unwanted pressure pointsor warpage on the wafer 123 during the polishing process, and helps tomaintain uniform thickness of the wafer 123.

The substantial mechanical movement of the platen 110 and the polishinghead assembly 120 produces characteristic sounds within the chamber 100.FIG. 2A schematically illustrates a normally operating CMP process, andthe characteristic sounds, detected by a set of microphones 250, of thenormally operating CMP process in time domain and in frequency domain.The amplitude and frequency of sound inside the chamber 100 may dependon factors such as, for example, rotational speed of the platen 110,rotational speed of the wafer 123, oscillation frequency of the head121, alignment between the platen 110 and the wafer 123, material at thewafer surface, thickness of a film at the wafer surface, materialimmediately underneath a film at the wafer surface, material of thewafer 123, thickness of the wafer 123, composition of the slurry 135,rate of flow of the slurry 135, material of the polishing pad 111, andcondition of the polishing pad 111, etc. Other factors determining theamplitude and frequency of sound inside the chamber 100 are contemplatedwithin the scope of the present disclosure. Although not seen in thefigures, in some embodiments the sound spectrum includes sounds offrequencies as low as fractions of a hertz (e.g., 0.01 Hz) tofrequencies as high as several megahertz (e.g., 200 MHz).

In some embodiments, if the parameters of the CMP process remain thesame, the sound spectrum of a CMP process remains generally the same. Onthe other hand, as the parameters change the sound spectrum shouldchange. For example, a change in material at the wafer surface becauseof removal of a film at the top surface of the wafer changes the soundspectrum depending on the material immediately underneath the film atthe top surface of the wafer in some embodiments. Other changes andanomalies in the CMP process may also result in a change in thecharacteristic sound spectrum associated with the CMP process. Forexample, a scratch on the wafer surface may result in a temporary changein composition of the slurry by temporarily adding particles of thematerial of the wafer surface to the slurry. These particles may getwashed away as more slurry is added to the process and the processcontinues to operate. However, the temporary change in composition ofthe slurry may be sufficient to temporarily change the sound spectrumassociated with the CMP process.

FIG. 2B schematically illustrates an anomalously operating CMP process,and the characteristic sounds, detected by a set of microphones 250, intime domain and frequency domain. FIG. 2C depicts a sound spectrum ofthe anomalously operating CMP process from FIG. 2B overlaid on the soundspectrum of the normally operating CMP process from FIG. 2A.

Specifically, FIG. 2B depicts a change in composition of the slurry 123because of an occurrence of a micro-scratch on the wafer surface. Theadditional particles from the wafer surface and a localized change inthickness of the top layer of the wafer surface results in a soundspectrum that is different from the sound spectrum of the normallyproceeding CMP shown in FIG. 2A. As can be seen in FIG. 2C, some partsof the sound spectrum of the CMP process remain unchanged, while otherparts of the sound spectrum of the CMP process undergo substantialchange because of the micro-scratch.

Changes in sound spectrum, thus, indicates a change in parameters of theCMP process in some embodiments. In some cases, the change occurs as theprocess continues to operate. For example, a change in sound spectrumoccurs because of a change in thickness of the top layer of the wafer.However, certain changes, such as the one depicted in FIG. 2B because ofthe micro-scratch, may not be expected in a normal CMP process. Theoccurrence of a desired event or an anomalous event in a CMP process maybe detected by continuously analyzing the sound spectrum to detectpatterns in the sound spectrum during the CMP process and comparing thedetected patterns with known or learned patterns of sound spectrum.Anomalous events include, without limitation, a micro-scratch on thewafer surface from slurry abrasive; abnormal positioning or thickness ofthe polishing pad; abnormal leveling of the polishing pad; the platen orthe wafer; degradation of the polishing pad, etc.

FIG. 3 schematically illustrates an apparatus for monitoring a CMPprocess, in accordance with an embodiment of the present disclosure. Inan embodiment, the apparatus for monitoring the CMP process includes aset of microphones 250 disposed in or adjacent to the chamber for theCMP apparatus depicted in FIG. 1 . The apparatus for monitoring the CMPprocess further includes a signal processor 310 operatively connected tothe set of microphones 250 and configured to receive and process anelectrical signal from the set of microphones 250. The apparatus furtherincludes a process controller 320 operatively connected to the signalprocessor 310 and configured to receive a feedback signal from thesignal processor 310 and control parameters of the CMP process based onthe feedback signal.

In an embodiment, the set of microphones 250 includes one or moremicrophones chosen to optimize the sound collected from the CMP process.For example, the set of microphones 250 may include a single wide-bandmicrophone designed to detect sound in the range of about 0.01 Hz toabout 200 MHz. In some embodiments, the set of microphones 250 includesseveral narrow-band microphones tailored to detect specific frequencyranges. For example, the set of microphones 250 may include one or moreinfrasonic microphones designed to detect sounds of frequencies fromabout 0.01 Hz to about 20 Hz, one or more acoustic microphones designedto detect sounds of frequencies from about 20 Hz to about 20 kHz and oneor more ultrasonic microphones designed to detect sounds from about 20kHz to about 200 MHz. An example of infrasonic microphones includes, butis not limited to, an electret condenser microphone. Examples ofacoustic and ultrasonic microphones include, but are not limited to,piezoelectric microphones, capacitive microphones, moving coilmicrophones, or optoacoustic microphones.

In an embodiment, the set of microphones 250 is disposed at a locationwithin or adjacent to the chamber 100 to maximize the detected sound. Inan embodiment, the set of microphones 250 is disposed on or adjacent toa wall of the chamber 100. In some embodiments, the set of microphones250 is distributed throughout the chamber 100. For example, some of themicrophones in the set of microphones 250 may be placed on the chamberwall 100, while others may be placed underneath the platen 110 and yetothers may be placed on the top-side of the carrier 122 away from thewafer 123. In some embodiments, the distribution and placement of themicrophones is optimized based on the frequency and amplitude of soundanticipated at a particular location within the chamber 100. It isexpected that higher frequency sounds are directional and attenuate in aradial direction. For such sounds, narrow-band microphones designed todetect directional sounds are used in certain embodiments. In otherembodiments, the set of microphones 250 are placed outside the chamber100 at locations where sound from the chamber 100 can be detected.

Referring to FIG. 3 , in an embodiment, an infrasonic microphone isdisposed on or adjacent to a top wall of the chamber 100, a set ofnarrow-band acoustic microphones collectively spanning the entireacoustic spectrum (i.e., about 20 Hz to about 20 kHz) is disposed on oradjacent to sidewalls of the chamber 100, a set of narrow-bandultrasonic microphones collectively spanning a sound spectrum rangingfrom about 20 kHz to about 200 MHz is disposed on a bottom-side (notexplicitly shown) of the platen 110 (away from the pad 111), and a setof narrow-band ultrasonic microphones collectively spanning a soundspectrum ranging from about 20 kHz to about 200 MHz is disposed on atop-side (not explicitly shown) of the carrier 122 (away from wafer123).

In an embodiment, each of the microphones in the set of microphones 250is hard-wired to the signal processor 310 so as to transmit electricalsignals corresponding to the sound it detects. In another embodiment,each of the microphones in the set of microphones 250 transmits theelectrical signals corresponding to the sound it detects wirelessly tothe signal processor 310. For example, the microphones transmit theelectrical signals to the signal processor 310 using a wirelesscommunication protocol such as Bluetooth, or IEEE 802.11 (Wi-Fi) incertain embodiments. Other types of wireless communication protocols,including proprietary protocols, are contemplated within the scope ofthe present disclosure.

In an embodiment, the signal processor 310 includes a non-transitorycomputer-readable memory and a processor configured to receive theelectrical signals from the set of microphones 250, process theelectrical signals and analyze the electrical signals. Signal processingincludes, without limitation, synchronizing the electrical signals andfiltering the electrical signals to reduce noise.

In some embodiments, the set of microphones 250 is spatially dispersedwithin or adjacent to the chamber 100 and unsynchronized to facilitateinstallation of the microphones. In such embodiments, synchronization ofthe electrical signals received from the various microphones at thesignal processor 310 may be performed if necessary. In an embodiment,synchronizing the electrical signals includes generating a timing signalhaving a frequency substantially disjoint from the frequencies of theunsynchronized electrical signals, transmitting the timing signal toeach of the microphones, receiving a combined signal including acombination of the timing signal and a corresponding unsynchronizedelectrical signal from each of the microphones, and separating each ofthe combined signals to recover the unsynchronized electrical signal andthe timing signal and aligning the unsynchronized signals according tothe recovered timing signal to produce synchronized electrical signals.In such embodiments, it is contemplated that frequency of the timingsignal is chosen. Therefore, any overlay in energy with theunsynchronized electrical signals can be negligible to avoid drowningout information contained in the electrical signals. For example, insome embodiments, the timing signal has a frequency in the gigahertz(GHz) region where the electrical signals received from the set ofmicrophones 250 have very little or no energy.

In an embodiment, all of the microphones in the set of microphones 250are synchronized using a signal from the process controller 320. Forexample, the process controller transmits an “initiate detection” signalto each of the microphones simultaneously and each of the microphonesbegins detecting the sound signals in response to receiving the“initiate detection” signal in some embodiments. The process controller320 synchronizes the “initiate detection” signal with a start of theoperation of the CMP process in some embodiments. Thus, sound detection(and thereby generation of electrical signals) at each of themicrophones is synchronized with the start of the CMP process. Othermethods of synchronizing the electrical signals from the unsynchronizedmicrophones are contemplated within the scope of the present disclosure.

In an embodiment, the signal processor 310 is configured to filter theelectrical signals received from each of the set of microphones 250 toreduce ambient sound and noise so as to improve the signal to noiseratio (SNR). Various methods for filtering electrical signals are knownin the art and will not be detailed herein.

Signal analysis includes, without limitation, sound source positiondetection, time domain analysis of the sound spectrum, conversion of theelectrical signal from time domain to frequency domain, frequency domainanalysis of the sound spectrum, decomposition of the signals, patternrecognition, pattern comparison, etc.

In an embodiment, the signal processor 310 is configured to detect theposition of a source of sound. The source of sound may be detected usinga triangulation algorithm. For example, in cases where the microphonesof the set of microphones 250 are unsynchronized, the set of microphones250 are composed to have three or more microphones having identicalband-width and frequency sensitivities disposed around the chamber 100in some embodiments. The band-width and central frequency of the threeor more microphones are chosen, for example, following a frequencydomain analysis of the sound spectrum during the CMP process, tomaximize the strength of the sound signals received or detected at thethree or more microphones in some embodiments. Following asynchronization process, a time difference in the arrival of thespecific sound received at the three or more microphones may then beused to calculate the distance of the source of the sound from each ofthe three or more microphones, which in turn is used to calculate thelocation of the source of sound.

In embodiments where the microphones from the set of microphones 250 aresynchronized, e.g., through the process controller, the signal processor310 is configured to receive the synchronized electrical signals,process the signals to detect a common pattern in signals frommicrophones that detect sounds in an overlapping frequency band andcalculate a time difference between the common pattern coming fromdifferent microphones. A position of a source of that common pattern iscalculated based on the time difference by using the positions of themicrophones providing the common pattern.

In various embodiments, algorithms such as, for example, Fouriertransform (e.g., FFT, DFT, etc.), Laplace transform, or wavelettransform are employed to convert the time domain signals to frequencydomain signals.

Pattern recognition may include a model-based method or amachine-learning method. In an embodiment, a model-based method is usedfor recognizing patterns in the sound spectrum following synchronizationof all electrical signals received from the set of microphones 250. Inthe model-based method, a model for sound spectrum for a normal CMPprocess (with a given set of parameters) is generated using regressionanalysis performed over several normal cycles of the CMP process. Forexample, the signal processor 310 recognizes a micro-scratch formed onthe wafer surface during a CMP process for planarizing a shallow trenchbased on a model for sound spectra for a CMP process for planarizing ashallow trench by recognizing a deviation from the model sound spectrain some embodiments.

In an embodiment, the signal processor 310 is configured to “learn”normal sound spectra, abnormal sound spectra, and sound patternsassociated with a desired normal event by providing feedback to thesignal processor 310 about normality or abnormality (and the cause ofabnormality) of the process as well as by indicating a specific event ina normal cycle. Examples of specific events include, but are not limitedto, reaching an end-point, and reaching a desired thickness of the topfilm, etc. Patterns of sound spectra may depend on factors such asmaterial of the wafer surface (aluminum, copper, tungsten, silicondioxide, and silicon nitride, etc.), layout of the surface (devicepattern on the top surface, pattern density, etc.) and composition ofthe slurry.

For example, in some embodiments, the signal processor 310 “learns” thata normal CMP process for planarizing a shallow trench has a particularpattern, viz., normal pattern, and a micro-scratch formed on the wafersurface during a CMP process for planarizing a shallow trench results inthe normal pattern changing a particular way based on recognizingpatterns of the sound spectra of the CMP process over a large number ofprocess cycles.

In an embodiment, once a pattern for the sound spectra (interchangeablyreferred to herein as the “sound pattern”) is recognized, the signalprocessor 310 generates a feedback signal including information relatingto the CMP process based on the sound pattern, and transmits thefeedback signal to the process controller 320. The feedback signal maysimply be an “all OK” signal if the sound pattern indicates a normalprocess. In an embodiment, the feedback signal for a normal processadditionally includes indication that a predetermined event such as, forexample, an end-point, or a desired thickness, has occurred. On theother hand, if the pattern of sound spectra indicates an abnormalprocess, the feedback signal indicates to the process controller 320that an abnormal or anomalous event has occurred. In such cases, thefeedback signal includes information about the anomalous eventindicating, for example, the type of event and the source of anomaly.

In an embodiment, the process controller 320 includes a non-transitorycomputer-readable memory and a processor configured to receive thefeedback signal from the signal processor, analyze the feedback signaland control various parameters of the CMP process by transmittingcommands to various processing units of the CMP apparatus including, butnot limited to, the platen 110, the polishing head assembly 120, theslurry supply system 130 and the pad conditioner 140. The parameters ofthe CMP process that are controlled by the process controller 320, insome embodiments, include, without limitation, rotational velocity ofthe platen 110, flow rate and composition of the slurry 135 beingsupplied on the polishing pad 111, pressure at which the wafer 123contacts the polishing pad 111, conditioning of the polishing pad 111,rotational velocity of the wafer carrier 122, oscillation frequency ofthe polishing head 121, etc. In an embodiment, the process controller320 is further configured to communicate with the set of microphones 250to, for example, facilitate synchronizing the microphones.

In an embodiment, upon receiving a feedback signal that an event (normalor anomalous) has occurred, the process controller 320 analyzes thefeedback signal and initiates a predetermined action in response to theoccurrence of event. In case of a normal, desired event such as anend-point of the CMP process or a change in material, the processcontroller 320 initiates action to stop the process. In an embodiment,the feedback signal includes information that the material removal rateis lower than normal. A low removal rate may occur because of a changein material at the surface of the wafer or because the slurry flow rateis not optimized. Thus, if the feedback signal, based on the soundpattern analyzed by the signal processor 310, indicates that thedecrease in removal rate has occurred because of a change in material atthe wafer surface, and a change in material is the desired outcome ofthe process, then the process controller 320 determines that the processis continuing normally and no corrective action is needed.

In case of an anomalous event, the process controller 320 determineswhether a corrective action will normalize the process following theanomalous event and determines which of the process parameters is bestsuited for normalizing the process based on the feedback signal in someembodiments. For example, if the feedback signal indicates that thedecrease in removal rate has occurred because of non-optimal slurry flowrate, the process controller 320 transmits a command to the slurrysupply system 130 to change the slurry flow rate.

FIG. 4 depicts a flow chart for a method of monitoring a CMP process. Inan embodiment, the method for monitoring a CMP process includes, atS420, detecting a sound signal generated during a CMP process; at S430,processing the sound signal; at S440, recognizing patterns of the soundsignal to detect an occurrence of a predetermined event; at S450generating a feedback signal including information associated with thepredetermined event; and at S410 controlling parameters of the CMPprocess based on the information in the feedback signal.

Detecting the sound signal is performed using a set of microphonesdisposed in the chamber enclosing the CMP apparatus in some embodiments.The set of microphones includes one or more microphones chosen tomaximize the sound collected from the CMP process. For example, a singlewide-band microphone designed to detect sound in the range of about 0.01Hz to about 200 MHz is disposed at a suitable location in the CMPprocess chamber. Alternatively, or in addition, several narrow-bandmicrophones tailored to detect specific frequency ranges are employed.In an embodiment, the set of microphones is disposed at a locationwithin the chamber to maximize the detected sound. For example, themicrophones are disposed on the chamber wall, the bottom-side of theplaten and/or the top-side of the wafer carrier.

The detected sound signal is converted into an electrical signal andtransmitted to a signal processor for processing the electrical signalscorresponding to the sound detected by the set of microphones. The term“sound signals” is interchangeably used herein to indicate theelectrical signals corresponding to the sound detected by the set ofmicrophones. In an embodiment, the signal processor includes anon-transitory computer-readable memory and a processor configured toreceive the sound signals, process the sound signals and analyze thesound signals. Processing the sound signals may include, withoutlimitation, receiving the sound signals, synchronizing the receivedsignals, and filtering the synchronized signals to reduce noise.

In some embodiments, synchronization of the received signals is achievedby generating a timing signal having a frequency substantially disjointfrom the frequencies of the unsynchronized electrical signals,transmitting the timing signal to each of the microphones, receiving acombined signal including a combination of the timing signal and acorresponding unsynchronized electrical signal from each of themicrophones, and separating each of the combined signals to recover theunsynchronized electrical signal and the timing signal and aligning theunsynchronized signals according to the recovered timing signal toproduce synchronized electrical signals. In such embodiments, it iscontemplated that frequency of the timing signal is chosen such thatthere is negligible, if any, overlap in energy with the unsynchronizedelectrical signals so as to avoid drowning out information contained inthe electrical signals.

In some embodiments, the microphones are synchronized using asynchronization signal from a process controller configured to controlvarious process parameters of the CMP process. For example, the processcontroller transmits a synchronization signal indicating a start-time ofthe CMP process, thereby commanding the set of microphones to initiatesound detection.

Analyzing includes, without limitation, detecting of sound sourceposition, analyzing the sound spectrum in time domain, converting theelectrical signal from time domain to frequency domain, analyzing thesound spectrum in frequency domain, decomposing the signals, recognizingpatterns in the signal and comparing the recognized patterns with knownor learned patterns, etc.

The source of sound may be detected using a triangulation algorithm. Inan embodiment, band-width and central frequency of the three or moremicrophones is chosen, following a frequency domain analysis of thesound spectrum during the CMP process, to maximize the strength of thesound signals received or detected at the three or more microphones.Following a synchronization process, a time difference in the arrival ofthe specific sound received at the three or more microphones may then beused to calculate the distance of the source of the sound from each ofthe three or more microphones, which may in turn be used to calculatethe location of the source of sound. Other methods for detecting asource of sound using unsynchronized spatially dispersed microphones arecontemplated within the scope of the present disclosure.

Recognizing the patterns of sound signals may be achieved either by amodel-based method or a machine-learning method. In an embodiment, amodel for sound spectrum for a normal CMP process (with a given set ofparameters) is generated using regression analysis performed overseveral normal cycles of the CMP process. In such embodiments, apredetermined normal event is recognized based on the model, and anabnormal event is recognized by recognizing a deviation from the modelsound spectra.

In an embodiment, normal sound spectra abnormal sound spectra, and soundpatterns associated with a desired normal event are learned based on afeedback relating to the normality, abnormality (and the cause ofabnormality) and indications relating to the desired normal event. Insuch embodiments, events are recognized based on comparison with the“learned” patterns.

Once a pattern is recognized, the information associated with therecognized pattern is used to generate a feedback signal which includesinformation relating to the event (normal or abnormal) corresponding tothe recognized pattern. In cases where the detected event is a desiredevent, e.g., an end-point, a desired change in thickness, or a desiredchange in material, the information from the feedback signal may be usedto terminate the process, or change certain parameters of the process toenable the process to continue normally as desired. In cases where thedetected event is abnormal or anomalous, the information from thefeedback signal is used to control the parameters for the CMP process toeither terminate the CMP process or provide a corrective action thatnormalizes the CMP process following the abnormal or anomalous event.

The parameters of the CMP process that may be controlled include,without limitation, rotational velocity of the platen, flow rate andcomposition of the slurry being supplied on the polishing pad, pressureat which the wafer contacts the polishing pad, conditioning of thepolishing pad, rotational velocity of the wafer carrier, and oscillationfrequency of the polishing head, etc.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

According to one aspect of the present disclosure, an apparatus forchemical mechanical polishing of a wafer includes a process chamber, arotatable platen disposed substantially horizontally inside of theprocess chamber, a polishing pad disposed on the platen, a wafer carrierdisposed on the platen, the wafer carrier including a wafer holderconfigured to retain the wafer, the wafer being held upside down on thepad during operation of the apparatus, a slurry supply port configuredto supply slurry on the platen, a process controller configured controloperation of the apparatus, a set of microphones disposed in or adjacentto the process chamber, the set of microphones arranged to detect soundin the process chamber during operation of the apparatus and transmit anelectrical signal corresponding to the detected sound, and a signalprocessor configured to receive the electrical signal from the set ofmicrophones, process the electrical signal to enable detection of anevent during operation of the apparatus, and in response to detectingthe event, transmit a feedback signal to the process controller. Theprocess controller is further configured to receive the feedback signaland initiate an action based on the received feedback signal. In one ormore of the foregoing and following embodiments, the set of microphonesincludes microphones configured to detect sounds with frequency in arange of about 0.01 Hz to about 200 MHz. In an embodiment, the actionincludes at least one selected from the group consisting of changing arotational velocity of the rotatable platen, changing a flow rate andcomposition of the slurry being supplied through the slurry port, andchanging a pressure at which the wafer contacts the polishing pad. In anembodiment, the set of microphones is configured to transmit theelectrical signal using a wireless communication protocol. In anembodiment, the signal processor is further configured to perform atleast one selected from the group consisting of filtering the electricalsignal to remove noise or ambient sound from the detected sound,detecting a position of a source of the detected sound, processing theelectrical signal in time domain or in frequency domain, and recognizingpatterns in the detected sound as corresponding to predetermined eventsduring the operation of the apparatus. In one or more of the foregoingand following embodiments, the recognizing patterns includes matchingpatterns of sounds with known events based on event models or usingpreviously learned correspondence between patterns of sounds and events.

According to another aspect of the present disclosure, a method ofoperating an apparatus for chemical mechanical polishing includesdetecting sound in a process chamber of the apparatus during operationof the apparatus and transmitting an electrical signal corresponding tothe detected sound to a signal processor using a set of microphones,processing, at the signal processor, the electrical signal received fromthe set of microphones to enable detection of an event during operationof the apparatus, and in response to detecting the event, transmitting afeedback signal corresponding to the detected event to a processcontroller, and initiating, by the process controller, an action basedon the received feedback signal. In one or more of the foregoing andfollowing embodiments, the action includes changing one or moreparameters of the chemical mechanical polishing. In one or more of theforegoing and following embodiments, the set of microphones includesmicrophones configured to detect sounds with a frequency in the range ofabout 0.01 Hz to about 200 MHz. In an embodiment, the parameters includeat least one selected from the group consisting of a rotational velocityof a rotatable platen, a flow rate and composition of a slurry beingsupplied on an polishing pad disposed on the rotatable platen, and apressure at which a wafer contacts the polishing pad. In an embodiment,the event is at least one selected from the group consisting of an endpoint of the chemical mechanical polishing; a scratch on a wafersurface, degradation of an polishing pad, abnormal leveling of thepolishing pad or the wafer, presence of an abrasive particle on thepolishing pad or the wafer surface, and change in material at the wafersurface. In one or more of the foregoing and following embodiments, theprocessing the electrical signal includes at least one selected from thegroup consisting of filtering the electrical signal to remove noise orambient sound from the detected sound, detecting a position of a sourceof the detected sound, processing the electrical signal in time domainor in frequency domain, and recognizing patterns in the detected soundas corresponding to predetermined events during the operation of theapparatus. In an embodiment, the recognizing patterns includes matchingpatterns of sounds with known events based on event models or usingpreviously learned correspondence between patterns of sounds and events.In an embodiment, the set of microphones is configured to transmit theelectrical signal using a wireless communication protocol.

According to yet another aspect of the present disclosure, a system formonitoring a chemical mechanical polishing process includes a processcontroller configured control parameters of the process, a set ofmicrophones disposed in or adjacent to a process chamber of an apparatusfor chemical mechanical polishing, the set of microphones arranged todetect sound in the process chamber during the process and transmit anelectrical signal corresponding to the detected sound, and a signalprocessor configured to receive the electrical signal from the set ofmicrophones, process the electrical signal to enable detection of anevent during operation of the apparatus, and in response to detectingthe event, transmit a feedback signal corresponding to the detectedevent to the process controller. In an embodiment, the processcontroller is further configured to receive the feedback signal andinitiate a change in one or more parameters of the process based on thereceived feedback signal. In one or more of the foregoing and followingembodiments, the one or more parameters of the process includes at leastone selected from the group consisting of a rotational velocity of arotatable platen, a flow rate and composition of a slurry being suppliedon an polishing pad disposed on the rotatable platen, and a pressure atwhich a wafer contacts the polishing pad. In an embodiment, the set ofmicrophones includes microphones configured to detect sounds with afrequency in the range of about 0 Hz to about 200 MHz. In an embodiment,the set of microphones is configured to transmit the electrical signalusing a wireless communication protocol. In one or more of the foregoingand following embodiments, the signal processor is further configured toperform at least one selected from the group consisting of filtering theelectrical signal to remove noise or ambient sound from the detectedsound, detecting a position of a source of the detected sound,processing the electrical signal in time domain or in frequency domain,and recognizing patterns in the detected sound as corresponding topredetermined events during the operation of the apparatus. In anembodiment, the recognizing patterns includes matching patterns ofsounds with known events based on event models or using previouslylearned correspondence between patterns of sounds and events.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A system for chemical mechanical polishing of awafer; the system comprising: a process chamber; a rotatable platendisposed substantially horizontally inside of the process chamber; apolishing pad disposed on the rotatable platen; a wafer carrier disposedon the rotatable platen, the wafer carrier configured to retain thewafer; a slurry supply port configured to supply slurry to the rotatableplaten; a process controller configured to control the operation of thesystem; a set of microphones including at least one infrasonicmicrophone, at least one acoustic microphone, and at least oneultrasonic microphone disposed in or around the process chamber; the setof microphones arranged to detect sound in the process chamber duringthe operation of the system and to transmit an electrical signalcorresponding to the detected sound; and a signal processor configuredto receive the electrical signal from the set of microphones, to processthe electrical signal to enable detection of an event during theoperation of the system, and in response to detecting the event,transmit a feedback signal to the process controller, whereinband-widths and central frequencies of the set of microphones areconfigured to maximize a strength of sound signals received or detectedat the set of microphones, wherein the process controller is furtherconfigured to receive the feedback signal and initiate an action basedon the received feedback signal, calculate a distance of a source of thesound from each of the set of microphones, and calculate a location ofthe source of the sound, wherein the signal processor is furtherconfigured to recognize patterns in the detected sound as correspondingto predetermined events and matching patterns of sounds with knownevents based on event models or using previously learned correspondencebetween patterns of sounds and events, a frequency range of soundsdetected by each microphone of the set of microphones is different, andwherein the at least one infrasonic microphone is disposed on oradjacent to a top wall of the process chamber, the at least one acousticmicrophone is disposed on or adjacent to sidewalls of the processchamber, and the at least one ultrasonic microphone includes a firstultrasonic microphone disposed on a bottom-side of the rotatable platenand a second ultrasonic microphone disposed on a top-side of the wafercarrier.
 2. The system of claim 1, wherein the action comprises at leastone selected from the group consisting of changing a rotational velocityof the rotatable platen, changing a flow rate and composition of theslurry being supplied through the slurry port, and changing a pressureat which the wafer contacts the polishing pad.
 3. The system of claim 1,wherein the detected event is at least one selected from the groupconsisting of an end point of a process, a scratch on wafer surface,degradation of the polishing pad, abnormal leveling of the polishing pador the wafer, presence of an abrasive particle on the polishing pad orwafer surface, and change in material at wafer surface.
 4. The system ofclaim 1, wherein the set of microphones is configured to transmit theelectrical signal using a wireless communication protocol.
 5. The systemof claim 1, wherein the signal processor is further configured toperform at least one selected from the group consisting of filtering theelectrical signal to remove noise or ambient sound from the detectedsound, detecting a position of a source of the detected sound, andprocessing the electrical signal in a time domain and in a frequencydomain.
 6. The system of claim 1, wherein the at least one infrasonicmicrophone is designed to detect sounds of frequencies from about 0.01Hz to about 20 Hz, the at least one acoustic microphone is designed todetect sounds of frequencies from about 20 Hz to about 20 kHz, and theat least one ultrasonic microphone is designed to detect sounds fromabout 20 kHz to about 200 MHz.
 7. A method of operating an apparatus forchemical mechanical polishing, the method comprising: placing a set ofmicrophones including at least three microphones in or around a processchamber, wherein a rotatable platen is disposed substantiallyhorizontally inside the process chamber, a wafer carrier is disposed onthe rotatable platen and configured to retain a wafer for polishing,wherein the set of microphones including at least one infrasonicmicrophone, at least one acoustic microphone, and at least oneultrasonic microphone, and wherein the at least one infrasonicmicrophone is disposed on or adjacent to a top wall of the processchamber, the at least one acoustic microphone is disposed on or adjacentto sidewalls of the process chamber, and the at least one ultrasonicmicrophone includes a first ultrasonic microphone disposed on abottom-side of the rotatable platen and a second ultrasonic microphonedisposed on a top-side of the wafer carrier; adjusting band-widths andcentral frequencies of the at least three microphones so that a strengthof sound signals received or detected at the microphones are maximized;detecting sound in the process chamber of the apparatus during anoperation of the apparatus using the at least three microphones andobtaining electrical signals corresponding to the detected sounds fromthe at least three microphones, the electrical signals beingunsynchronized with each other; combining unsynchronized electricalsignals with a timing signal received from a signal processor;transmitting a combined signal including the timing signal and theunsynchronized electrical signals to the signal processor using the setof microphones; processing, at the signal processor, the electricalsignal received from the set of microphones to enable detection of anevent during the operation of the apparatus, and in response todetecting the event, transmitting a feedback signal corresponding to thedetected event to a process controller, wherein the process controllercalculates a distance of a source of the sound from each of the at leastthree microphones, and a location of the source of the sound; andinitiating, by the process controller, an action based on a receivedfeedback signal, wherein the action comprises changing one or moreparameters of the chemical mechanical polishing, wherein processing theelectrical signal comprises recognizing patterns in the detected soundas corresponding to predetermined events during the operation of theapparatus and matching patterns of sounds with known events based onevent models or using previously learned correspondence between patternsof sounds and events.
 8. The method of claim 7, wherein the parameterscomprise at least one selected from the group consisting of a rotationalvelocity of the rotatable platen, a flow rate and composition of aslurry being supplied on a polishing pad disposed on the rotatableplaten, and a pressure at which a wafer contacts the polishing pad. 9.The method of claim 7, wherein the detected event is at least oneselected from the group consisting of an end point of the chemicalmechanical polishing, a scratch on a wafer surface, degradation of apolishing pad, abnormal leveling of the polishing pad or the wafer,presence of an abrasive particle on the polishing pad or the wafersurface, and change in material at the wafer surface.
 10. The method ofclaim 7, wherein processing the electrical signal comprises at least oneselected from the group consisting of filtering the electrical signal toremove noise or ambient sound from the detected sound, detecting aposition of a source of the detected sound, and processing theelectrical signal in a time domain or in a frequency domain or both. 11.The method of claim 7, wherein the set of microphones is configured totransmit the electrical signal using a wireless communication protocol.12. The method of claim 7, wherein electrical signals output from the atleast, three microphones are indicative of frequency range of soundsdetected by the at least three microphones and a frequency range ofsounds detected by each microphone of the at least three microphones isdifferent.
 13. The method of claim 7, wherein the set of microphones isconfigured to detect sounds with a frequency in the range of about 0.01Hz to about 200 MHz.
 14. An apparatus for monitoring a chemicalmechanical polishing process, the apparatus comprising: a processcontroller configured to control parameters of the process; a set ofmicrophones including at least three microphones disposed in or around aprocess chamber of an apparatus for chemical mechanical polishing, theset of microphones arranged to detect sound in the process chamberduring the process and transmit an electrical signal corresponding tothe detected sound, wherein a rotatable platen is disposed inside theprocess chamber, a wafer carrier is disposed on the rotatable platen andconfigured to retain a wafer for polishing, wherein the set ofmicrophones including at least one infrasonic microphone, at least oneacoustic microphone, and at least one ultrasonic microphone, and whereinthe at least one infrasonic microphone is disposed on or adjacent to atop wall of the process chamber, the at least one acoustic microphone isdisposed on or adjacent to sidewalls of the process chamber, and the atleast one ultrasonic microphone includes a first ultrasonic microphonedisposed on a bottom-side of the rotatable platen and a secondultrasonic microphone disposed on a top-side of the wafer carrier, andwherein band-widths and central frequencies of the at least threemicrophones are configured to maximize a strength of sound signalsreceived or detected at the at least three microphones; and a signalprocessor configured to receive the electrical signal from the set ofmicrophones, process the electrical signal to enable detection of anevent during an operation of the apparatus, and in response to detectingthe event, transmit a feedback signal corresponding to the detectedevent to the process controller, wherein the process controller isfurther configured to receive the feedback signal and initiate a changein one or more parameters of the process based on the received feedbacksignal, calculate a distance of a source of the sound from each of theat least three microphones, and calculate a location of the source ofthe sound, the at least three microphones are configured to outputelectrical signals that are synchronized with each other based on asynchronization signal output from the process controller, and eachmicrophone of the at least three microphones is configured to detectsound in response to receiving the synchronization signal, and afrequency range of sounds detected by each microphone of the at leastthree microphones is different, wherein the signal processor is furtherconfigured to recognize patterns in the detected sound as correspondingto predetermined events during the operation of the apparatus and matchthe patterns of sounds with known events based on event models or usingpreviously learned correspondence between patterns of sounds and events.15. The apparatus of claim 14, wherein the one or more parameters of theprocess comprise at least one selected from the group consisting of arotational velocity of the rotatable platen, a flow rate and compositionof a slurry being supplied on a polishing pad disposed on the rotatableplaten, and a pressure at which a wafer contacts the polishing pad. 16.The apparatus of claim 15, wherein the set of microphones comprisesmicrophones configured to detect sounds with a frequency in the range ofabout 0.01 Hz to about 200 MHz.
 17. The apparatus of claim 16, whereinthe at least one infrasonic microphone is designed to detect sounds offrequencies from about 0.01 Hz to about 20 Hz, the at least one acousticmicrophone is designed to detect sounds of frequencies from about 20 Hzto about 20 kHz, and the at least one ultrasonic microphone is designedto detect sounds from about 20 kHz to about 200 MHz.
 18. The apparatusof claim 14, wherein the set of microphones is configured to transmitthe electrical signal using a wireless communication protocol.
 19. Theapparatus of claim 14, wherein the signal processor is furtherconfigured to perform at least one selected from the group consisting offiltering the electrical signal to remove noise or ambient sound fromthe detected sound, detecting a position of a source of the detectedsound, processing the electrical signal in time domain or in frequencydomain.
 20. The apparatus of claim 14, wherein the detected event is atleast one selected from the group consisting of an end point of thechemical mechanical polishing, a scratch on a wafer surface, degradationof a polishing pad, abnormal leveling of the polishing pad or the water,presence of an abrasive particle on the polishing pad or the wafersurface, and change in material at the wafer surface.